This invention relates to improvements in hydraulic cementitious compositions such as concrete, mortar, grout and the like. More particularly, it relates to a cementitious composition which when mixed with water is capable of setting in a relatively short period of time to form a hard mass of high compressive strength without substantial shrinkage during setting and early hardening, which exhibits no substantial long-term shrinkage, and which possesses a high degree of impermeability to fluids.
The term "hydraulic cement" as used herein, is understood to include any cement which has the characteristic of hardening under water e.g., portland cement, blends of portland cement and natural cement, pozzolanic cements, slag cement, masonry cement, oil well cement, white portland cement, mixtures of portland cement and blast-furnace cement, and like materials. The term "concrete" is used to designate a mixture of hydraulic cement, aggregate, and water. This material sets to form a hard mass. The "aggregate" may be mineral or non-mineral, including naturally occurring materials such as sand, gravel or quarried rock, or manufactured aggregate such as expanded shale, clay, and the like. The term "mortar" is used herein to designate a mixture of hydraulic cement, fine aggregate and water. The term "grout" designates a mixture of hydraulic cement and water, and sometimes fine sands. Grouts normally have higher fluidity than mortars and can be pumped through pipe lines and forced into small spaces, for instance, into voids or cracks or porous concrete, or into spaces between preplaced aggregate or under machinery and heavy equipment. A more thorough description of cement technology suitable for an understanding of the background of the present invention can be found in Scientific American, April 1964, pages 80-90; Kirk-Othmer's Encyclopedia of Chemical Technology, 2d ed., Vol. 5, pages 684-710 (1964); and ACI Journal, August, 1970, pages 583-610.
In the construction industry, and particularly in the repair of concrete structures such as highways and structural walls and platforms, and the filling of voids and holes to form stable underpinnings or foundations for machinery and heavy equipment, there has been a long felt need for cementitious compositions which will set within a relatively short period of time into a hard mass with sufficient strength to withstand applied stresses and loads. In order to have commercial value, this type of cementitious composition must also have good bonding characteristics, early as well as long-term strength, practical field workability times, and be capable of withstanding freezing and thawing as well as the action of salts and the corrosive substances. Advantageously, the cementitious composition should also possess self-leveling properties so that the resultant material, when used in patching operations, will not create cavities or crown which would cause damage to the adjacent area of the structure. In addition, the applied composition should possess fluid barrier properties so that they are impermeable to liquid and vapor, particularly moisture.
Attempts have been made in the past to formulate cementitious compositions possessing one or more of the above properties, but such attempts, particularly when directed to the achievement of all of the foregoing desirable properties in a single composition, have met with only limited success. For example, compounds such as calcium chloride and other known setting-time accelerators have been incorporated in prior formulations, but the resulting products were characterized by undesirable shrinkage, high heat generation, and lack of resistance to freezing and thawing. Cement formulations made from plastics such as epoxy resins have been used for repairing concrete structures, but the lack of compatability between the plastic cement and concrete has precluded the extended use of this type of formulation. Other attempts at formulating improved cement compositions have been only partially successful mainly because the resulting products after mixing with water and placement using the customary techniques have failed to develop acceptable strengths within a desirably short period of time after setting without shrinkage. Furthermore, the failure of many of these products to achieve a high degree of impermeability to fluids, particularly water, has precluded their use in certain applications, e.g., grouting and water proofing, where that property is often critical. Thus, mixtures of portland cement and high alumina cement have been formulated as described in Chemistry and Industry, 1952, pages 2-7. Mixtures of various cements with gypsum and its dehydration products (which is known to affect the setting rate of the cement) are described in Budnikov, Fourth International Symposium on the Chemistry of Cement (1960), pages 469-477; Monfore, Journal PCA Research & Dev. Laboratories, May, 1964, pages 2-9; Greceanu, Proc, Conf. Silicate Industry, 9, 243-4 (1967); British Pat. Nos. 317,783 and 474,917; and U.S. Pat. Nos. 3,794,504 and 3,775,143.
Accordingly, it is an object of the present invention to provide a cementitious composition which when mixed with water will set within a relatively short period of time into a hard mass of sufficient strength and bonding characteristics to withstand applied stresses and loads.
Another object is to provide a cementitious composition which when mixed with water will set within a relatively short but practical field working time into a hard mass of high early and long-term strength without substantial shrinkage during either setting and early hardening or over the useful working life of the mass.
Another object is to provide a cementitious composition which when mixed with water will possess good leveling properties and set within a relatively short time into a hard mass which is capable of withstanding freezing and thawing and the action of salts and other corrosive substances, and which possesses high fluid barrier properties so as to be essentially impermeable to liquid and vapor, particularly water.
These and other objects of the invention as well as a fuller understanding of the advantages thereof, can be had by reference to the following detailed description and claims.